Charged particle beam exposure apparatus and exposure method

ABSTRACT

A charged particle beam exposure apparatus comprises a beam gun, a projection optics, a sample stage loaded with a sample wherein an image projected from the projection optics is to be formed, first marks are formed beforehand, and second marks are exposed to a charged particle beam with a first incident energy by the projection optics in the vicinity of the first marks, a detector detecting an electron signal from a region including the first and second marks, when the region is scanned with a second incident energy different from the first incident energy, a calculation circuit calculating a positional shift between the first and second marks from the detected signal, a correction circuit correcting a position of the first mark based on the calculated positional shift, and an exposure control circuit aligning a desired pattern based on the corrected position of the first mark.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromthe prior Japanese Patent Application No. 2001-067229, filed Mar. 9,2001, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a charged particle beam exposuretechnique for forming a desired pattern on a sample, particularly to acharged particle beam exposure apparatus and exposure method in which amark formed on a sample is used to adjust positions.

2. Description of the Related Art

An electron beam exposure apparatus shown in FIG. 1 has heretofore beenused as an apparatus for forming an LSI pattern on a semiconductorwafer. In FIG. 1, a reference numeral 1 denotes an electron gun, 2 a to2 c denote lenses, 3 denotes a first aperture, 4 a, 4 b denotedeflectors, 5 denotes a second aperture, 6 denotes a wafer, 7 denotes astage, 8 denotes a chip, 9 denotes a mirror, 10 denotes a laserinterferometer, 11 denotes a detector, 12 denotes an alignment mark, 13denotes a reflected electron, and 14 denotes an electron beam.Additionally, in many cases, the deflector 4 a for use in selecting abeam position of the second aperture 5 is disposed above and below thesecond aperture 5 to deflect a beam from an optical axis, and to returnthe deflected beam to the optical axis, but it is shown here in a simplemanner, i.e. only above the second aperture 5.

In the apparatus, when the pattern is exposed on the wafer 6, a relativeposition of the pattern on the wafer 6 with an optics needs to beadjusted. A method for this adjustment includes: using the mirror 9 andlaser interferometer 10 to constantly monitor the position of the stage7; scanning the alignment mark 12 formed for each chip 8 on the wafer 6with the electron beam 14; detecting the reflected electron 13 from themark 12 by the detector 11; and measuring the position of the mark 12.

However, this type of method has the following problems. That is, sincethe mark is detected for each mark 8 on the wafer 6, as shown by arrowsin FIG. 2A, a frequency of stage movement 20 increases. As a result, anexposure throughput decreases. Moreover, by an electron beam scanning21, a resist on the mark 12 is excessively exposed to light, aninsoluble region 22 is generated, and this causes dust generation.

As described above, in the conventional alignment in the electron beamexposure, since the frequency of the stage movement increases, thethroughput decreases. Moreover, another problem is that the resist onthe mark is excessively exposed to the electron beam scanned for thealignment, the dust generation is caused, and an alignment precision isdeteriorated.

Therefore, it has been necessary to realize a charged particle beamexposure apparatus and exposure method in which a resist can beprevented from being excessively exposed to the beam scanned for thealignment, and a throughput and the alignment precision can be enhanced.

BRIEF SUMMARY OF THE INVENTION

According to a first aspect of the present invention, there is provideda charged particle beam exposure apparatus, comprising:

a beam gun which emits a charged particle beam;

a projection optics which shapes the charged particle beam and projectsa desired pattern;

an incident energy control circuit which controls an incident energy ofthe projection optics;

a sample stage loaded with a sample in which an image projected from theprojection optics is to be formed, a plurality of first marks are formedbeforehand, and a plurality of second marks are exposed to the chargedparticle beam with a first incident energy by the projection optics inthe vicinity of the plurality of first marks;

a detector to detect an electron signal generated from a regionincluding the plurality of first marks and the plurality of secondmarks, when the region is scanned with a second incident energydifferent from the first incident energy;

a calculation circuit which calculates a positional shift amount betweenthe plurality of first marks and the plurality of second marks from thedetected electron signal;

a correction circuit which corrects positions of the plurality of firstmarks on the sample based on the calculated positional shift amount; and

an exposure control circuit which aligns the desired pattern based onthe corrected positions of the plurality of first marks.

According to a second aspect of the present invention, there is provideda charged particle beam exposure method comprising:

exposing a second mark on a sample to a charged particle beam with afirst incident energy based on a position of a first mark formed on thesample beforehand;

scanning a region including the first mark and the second mark with asecond incident energy by the charged particle beam;

detecting an electron signal generated from the sample by the scanning;

calculating a positional shift amount of the first mark and the secondmark from the detected electron signal;

correcting the position of the first mark on the sample based on thecalculated positional shift amount; and

aligning and exposing a desired pattern based on the corrected positionof the first mark.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a schematic configuration diagram showing a conventionalelectron beam exposure apparatus.

FIG. 2A is an explanatory view showing a problem of increased stagemovement in a conventional exposure method.

FIG. 2B is an explanatory view showing a problem of insolubility of aresist in the conventional exposure method.

FIG. 3A is a schematic configuration diagram showing an electron beamexposure apparatus according to a first embodiment of the presentinvention.

FIG. 3B is a block diagram showing a control system of the exposureapparatus of FIG. 3A.

FIGS. 4A to 4C are diagrams showing a movement of a main part of theexposure apparatus in the course of alignment in the first embodiment.

FIG. 5A is a sectional view of a wafer and shows a method of forming avernier pattern.

FIG. 5B is an explanatory view of a position relation between thevernier pattern and an alignment mark.

FIG. 5C is an explanatory view of a positional shift of the vernierpattern.

FIG. 5D is a sectional view of the wafer and shows an electron beamscanned to measure the positional shift.

FIG. 5E is a diagram showing a secondary electron beam intensity profileobtained as a result of the electron beam scanning of FIG. 5D.

FIG. 6 is a flowchart of an alignment method in the first embodiment.

FIG. 7 is an explanatory view showing a voltage contrast image of analignment mark pattern and vernier pattern, and an obtained positionalshift amount.

FIG. 8 is a diagram showing the stage movement for detecting the mark inthe first embodiment.

FIG. 9A is a diagram showing a relation between a second incident energyand a contrast during pattern observation with respect to a sample shownin FIG. 5A.

FIG. 9B is a photograph showing a contrast state in which an incidentenergy is 3 keV in FIG. 9A.

FIG. 10 is a flowchart of an alignment method in a modification exampleof the first embodiment.

FIG. 11 is a schematic configuration diagram showing an electron beamexposure apparatus according to a second embodiment.

FIGS. 12A to 12D are diagrams showing the movement of the main part ofthe exposure apparatus in the course of the alignment in the secondembodiment.

FIG. 13 is a flowchart of the alignment method in the second embodiment.

FIG. 14 is a schematic configuration diagram showing the electron beamexposure apparatus according to a third embodiment.

FIGS. 15A and 15B are diagrams showing a schematic configuration andexposure method of the electron beam exposure apparatus according to afourth embodiment.

FIGS. 16A and 16B are diagrams showing the schematic configuration andexposure method of the electron beam exposure apparatus according to themodification example of the fourth embodiment.

FIG. 17 is a schematic configuration diagram showing the electron beamexposure apparatus according to a fifth embodiment.

FIGS. 18A to 18C are explanatory views of a stage driving method in thefifth embodiment.

FIG. 19 is a schematic configuration diagram showing the electron beamexposure apparatus according to a sixth embodiment.

FIG. 20 is an explanatory view of the stage driving method in the sixthembodiment.

FIG. 21 is an explanatory view of the stage driving method in themodification example of the sixth embodiment.

FIG. 22 is a photograph for a view showing an alignment mark image andvoltage contrast image by a charged trace of the vernier pattern.

DETAILED DESCRIPTION OF THE INVENTION

An outline of the present invention will be described prior todescription of embodiments. In the present invention, an electron beamexposure system, and the like are used to expose a second mark (vernierpattern, and the like formed on a resist on a wafer) based on positioninformation of a first mark disposed on the wafer, a positional shiftbetween the vernier pattern and an alignment pattern (first mark) ismeasured, and the positional shift is corrected, so that the exposurewith a high-precision alignment is realized.

Moreover, positions of only some of the alignment marks formed on thewafer are detected, global alignment is performed, and other markpositions are calculated, so that a time required for the mark detectioncan be reduced as compared with a conventional method. As a result, aproductivity in electron beam exposure can be enhanced.

Furthermore, a second incident energy for measuring the positional shiftis set to be smaller than a first incident energy for forming thevernier pattern. Therefore, when a resist surface is scanned with a beamwith the second incident energy, a latent image in the resist exposedwith the first incident energy, that is, the vernier pattern isprevented from being superposed and exposed, and the latent image cantherefore be detected with a high precision. As a result, it is possibleto highly precisely measure a positional shift amount between thealignment mark and the vernier pattern, and further the alignmentexposure can be realized with the high precision.

Particularly, when the second incident energy is set to 3 keV or less,only about 0.3 μm from the surface is exposed with a several micrometersthick insulator film on the mark. Therefore, the insulator film surfacecan effectively be charged. Moreover, when a range of the charging beamhaving the second incident energy is set to be smaller than the resistfilm thickness, there is no fear that the pattern exposed with the firstincident energy is superposed and exposed in a depth direction.Moreover, when a bias voltage is applied to a sample in a method forchanging the first and second incident energies, an electron gun andelectron beam optics for the exposure, and an optics for detecting thepositions of the latent image and alignment mark can be used in common.As a result, an apparatus configuration can be simplified.

Additionally, a characteristic of the present invention lies in that thepositional shift between the vernier pattern and the alignment patternis measured by scanning the resist surface with the charging beam havinga relatively low energy. This principle will briefly be described.

A sample whose surface is formed of an insulating material is scannedwith the charging beam having a low energy, and the insulating materialsurface is charged. In this case, a potential distribution with asectional structure of the sample reflected therein is formed on thesample surface. On the other hand, a generation efficiency of asecondary electron generated by scanning the charging beam changes withthe surface potential distribution. As a result, when the sample havingthe surface formed of the insulating material is scanned with thecharging beam having the low energy, it is possible to obtain asecondary electron signal (voltage contrast image) with the sectionalstructure of the sample reflected therein.

Moreover, when a chemical, electrical, or physical change is generatedin the resist by the exposure, the surface potential distribution can beformed. For example, when a conductivity of the resist is changed by theexposure, the secondary electron signal obtained by scanning the resistsurface with the charging beam having the low energy indicates differentintensities in an exposed/unexposed portion. As a result, it is possibleto obtain the voltage contrast image corresponding to theexposed/unexposed portion of the resist.

Embodiments of the present invention will be described hereinafter withreference to the drawings.

First Embodiment

FIG. 3A is a schematic configuration diagram showing an electron beamexposure apparatus according to a first embodiment of the presentinvention, and FIG. 3B is a block diagram showing a control system ofthe apparatus. The present apparatus is an electron beam exposureapparatus of a variable shaped and character projection type with anacceleration energy of 5 keV. One characteristic of the presentinvention lies in that the conventional acceleration energy of about 50keV is changed to a low energy of 1 to 8 keV. Functions of respectivecomponents will be described hereinafter.

As shown in FIG. 3A, an electron beam 14 discharged from an electron gun1 is emitted onto a first aperture 3 by a capacitor lens 2 a. Theelectron beam 14 transmitted through the first aperture 3 is projectedonto a second aperture 5 by a projection lens 2 b. The first aperture 3has a rectangular opening, and the second aperture 5 has a characteropening to form a repeated pattern in addition to the rectangularopening. A shaping deflector 4 a deflects the electron beam 14 in anarbitrary position on the second aperture 5, so that a desired beamshape is realized.

A wafer (sample) 6 on a stage (sample base) 7 is irradiated with theelectron beam 14 transmitted through the second aperture 5 by areduction and objective lens 2 c. In this case, the electron beam 14 onthe wafer 6 is positioned by an objective deflector 4 b.

Additionally, in many cases, the deflector 4 a for use in selecting thebeam position on the second aperture 5 is disposed above and below thesecond aperture 5 in order to deflect the beam from an optical axis andreturn the deflected beam to the optical axis. However, only the upperdeflector is shown here for the sake of simplicity.

Mirrors 9 are disposed on two side surfaces of the stage 7 loaded withthe wafer 6, and a laser interferometer 10 for irradiating these mirrors9 with laser beams is disposed. The laser interferometer 10 constantlymeasures the position of the stage 7. Moreover, an electron detector 11is disposed opposite to the wafer 6. Furthermore, a reflected and asecondary electron signals generated when an alignment mark 12 formed onthe wafer 6 scanned with the electron beam are detected by the detector11.

The configuration described above is basically similar to that of theconventional apparatus, but the following characteristic configurationis added to the first embodiment. That is, the characteristic of thepresent apparatus lines in that a sample power supply 16 for applyingthe voltage to the wafer 6 via the stage 7 is disposed. Thereby, forexample, when a voltage of −4 kV is applied to the wafer 6, the incidentenergy to the wafer 6 can be set to a low energy of about 1 keV.

The control system of the exposure apparatus according to the firstembodiment will next be described with reference to FIG. 3B. The samecomponents as those of FIG. 3A are denoted with the same referencenumerals and redundant description is omitted. In FIG. 3B, a referencenumeral 109 denotes a beam control circuit, 110 denotes a beamposition/shape control circuit, 111 denotes a lens control circuit, 112denotes a detection amplifier, 113 denotes a calculation circuit, 114denotes a correction circuit, 115 denotes a stage (sample base) controlcircuit, 116 denotes an exposure control circuit, and 119 denotes anincident energy control circuit. Additionally, the lenses are omittedfrom FIG. 3B.

The beam control circuit 109 turns on/off the electron beam 14 based ona command of the exposure control circuit 116. The beam position/shapecontrol circuit 110 controls the deflector 4 a to determine an electronbeam shape, and controls the deflector 4 b to position the electron beam14 in a desired position on the wafer 6 based on the command of theexposure control circuit 116. The lens control circuit 111 controls thevoltage of the lens (not shown) based on the command of the exposurecontrol circuit 116, and projects the electron beam 14 with a reducedsize onto the wafer 6. The stage control circuit 115 moves the stage 7to the desired position based on the command of the exposure controlcircuit 116. The incident energy control circuit 119 controls theincident energy of the electron beam 14 incident upon the wafer 6 basedon the command of the exposure control circuit 116.

As described above, the electron beam 14 discharged from the electrongun 1 is shaped by the first aperture 3. Furthermore, the electron beam14 passed through the first aperture 3 is emitted to the desiredposition on the second aperture 5 by the deflector 4 a. Openings (notshown) having various shapes are formed in the second aperture 5. Thedeflector 4 a aligns the electron beam 14 with the desired opening onthe second aperture 5. Thereby, the electron beam 14 passed through thesecond aperture 5 is shaped in a desired shape. The electron beam 14passed through the second aperture 5 is projected in the reduced sizeonto the wafer 6 by the lens system (not shown). In this case, thedeflector 4 b positions the electron beam 14 in the desired position onthe wafer 6, so that the position is irradiated.

During exposure, the exposure control circuit 116 controls the electrongun 1, beam control circuit 109, beam position shape control circuit110, lens control circuit 111, and stage control circuit 115 to performthe exposure based on inputted wafer layout information 118 and drawingdata 117.

A control procedure using the control system constituted as describedabove will be described hereinafter.

A) The exposure control circuit 116 reads positions of a plurality ofalignment marks (first marks) to be detected on the wafer 6 from thewafer layout information 118. Subsequently, the exposure control circuit116 issues a command to the stage control circuit 115 and moves thestage 7. Thereby, the first mark on the wafer 6 is positioned in a rangewhich can be exposed to the electron beam.

B) Subsequently, the exposure control circuit 116 exposes the secondmark having a predetermined shape to the first incident energy in apredetermined position in the vicinity of the first mark. In this case,it is meant by the predetermined position in the vicinity of the firstmark that a position relation between the first and second marks ispredetermined and the marks are exposed with the predetermined relation.In this case, the exposure control circuit 116 stores a deflectedposition of the electron beam 14 and a stage position.

C) Then, the incident energy control circuit 119 is used to change thefirst incident energy to the second incident energy, and scans theregion including the first and second marks by the electron beam 14 withthe second incident energy. A secondary electron generated by thescanning is detected by the detector 11. The secondary electron signaldetected by the detector 11 is amplified by the detection amplifier 112,and transmitted as an image signal or a waveform signal to thepositional shift amount calculation circuit 113. The positional shiftamount calculation circuit 113 calculates the positional shift amountbetween the first and second marks from the transmitted image orwaveform signal. The calculated positional shift amount between thefirst and second marks is stored by the exposure control circuit 116.

D) The abovementioned steps A) to C) are performed for the number of allthe first marks on the wafer 6 to be detected.

E) When the steps A) to D) end, with respect to the plurality of firstmarks to be detected, the exposure control circuit 116 stores (a) thepositional shift amount between the first and second marks calculated bythe calculation circuit 113 and (b) the stage positions and beamdeflected positions when the respective first and second marks areexposed. The exposure control circuit 116 transmits these data (a), (b),and (c) the position relation of the first and second marks in design tothe correction circuit 114. The correction circuit 114 uses thetransmitted data (a), (b) and (c) to calculate a correction amount (d)of a position in which the second mark is exposed with respect to thedesigned position relation (c). The correction amount is calculated withrespect to all the first marks on the wafer 6 to be detected. Thereby,the correction amount (d) corresponding to a plurality of positions onthe wafer 6 can be obtained. The correction circuit 114 calculates afunction equation of the correction amount of a beam position withrespect to the position (X, Y) on the wafer 6 from the calculatedcorrection amount (d) corresponding to the plurality of positions on thewafer 6 in order to align the beam with the first mark on the wafer.

F) During drawing, the exposure control circuit 116 controls theelectron gun 1, beam control circuit 109, beam position shape controlcircuit 110, lens control circuit 111, and stage control circuit 115 toperform the exposure based on the inputted wafer layout information 118and drawing data 117. In this case, the exposure control circuit 116uses the function equation of the correction amount of the beam positionwith respect to the calculated position (X, Y) on the wafer 6 to correctthe beam position (X, Y) on the wafer 6 and perform the exposure.

Additionally, in the step E), the correction circuit 114 calculates thefunction equation of the correction amount of the beam position withrespect to the position (X, Y) on the wafer 6 from the calculatedcorrection amount (d) corresponding to the plurality of positions on thewafer 6 in order to align the beam with the first mark on the wafer 6.However, another method may also be used. For example, in order to alignthe beam with the first mark on the wafer 6, a function equation of thecorrection amount of the stage position with respect to the position (X,Y) on the wafer 6 may also be calculated.

Moreover, in the above description, the exposure of the second mark inthe step B, and the electron beam scanning by the second incident energyin the step C are alternately performed, but another order may also beused. For example, after the second mark is exposed to the firstincident energy with respect to all the first mark positions, theelectron beam may be scanned by the second incident energy with respectto all the first mark positions.

An alignment method in the first embodiment will next be described withreference to FIGS. 3B, 4A to 4C, 5A to 5E, and 6. FIGS. 4A to 4C arediagrams showing the movement of the exposure apparatus with thealignment, and FIGS. 5A to 5E are explanatory views of the alignmentmethod. A plurality of chips 8 are formed on the wafer 6 to be exposed,and the alignment mark 12 is disposed on each chip 8. Here, stepssubsequent to a step of loading the wafer 6 onto the stage 7 will bedescribed.

1) First, position information of all the marks 12 (first mark 201) tobe detected on the wafer 6 is read out from the wafer layout information118 of FIG. 3B (S1 of FIG. 6).

2) Subsequently, as shown in FIG. 4A, the wafer 6 is moved to theposition in which the electron beam exposure is possible, and thealignment exposure is performed based on the chip position calculated in1). In this case, as shown in FIG. 5B, a vernier pattern (second mark)202 is exposed to the first incident energy beside the alignment mark(first mark) 201 (corresponding to the mark 12) (S2 and S3 of FIG. 6).

Here, the mark is exposed by the first incident energy, while no voltageis applied from the sample power supply (i.e., while a voltage of 0 V isapplied). In this case, the incident energy to the resist is theacceleration voltage applied to the electron gun, and indicates 5 keV.Moreover, a section of the alignment mark 201 is shown in FIG. 5A. Thealignment pattern 201 is formed of a groove having a width of 0.5 μm anddepth of 0.5 μm on an Si substrate 200, and the pattern is coated withan insulator film 203 having a thickness of 0.5 μm. The insulator film203 is flatted, and coated with a resist 204 having a thickness of 0.2μm. Subsequently, the resist is irradiated with an electron beam 206 aand the latent image 202 is formed.

In FIG. 5A, the alignment pattern 201 is a recess formed on thesubstrate 200, but it may be a protrusion formed on the substrate 200and buried in the flatted insulator film 203.

3) Subsequently, as shown in FIG. 4B, the sample power supply 16 is usedto apply a voltage of 4 kV to the wafer 6. Thereby, the energy of theelectron beam 14 incident upon the wafer 6 decreases to 1 keV, and therange of the electron becomes smaller than the resist film thickness. Inthis case, as shown in FIG. 5C, the periphery of the vernier patternexposed in 3) is scanned. The section during the beam scanning is shownin FIG. 5D. Since the incident energy of an electron beam 206 b issmall, a scanned region 205 is not exposed down to a bottom thereof (S6to S8 of FIG. 6).

When the secondary electron signal obtained by the beam scanning isdetected, the voltage contrast image can be detected as shown in FIG.5E. It is possible to detect a relative positional shift amount of thealignment mark 201 and vernier pattern 202 from the voltage contrastimage. This step is performed on a plurality of positions, and acorrection value (Δx, Δy) is obtained in each position (S9 of FIG. 6).

FIG. 7 shows the voltage contrast image of an alignment mark pattern andvernier pattern. In FIG. 7, ΔX indicates the correction value.

4) The correction value obtained in 3) is considered in the chipposition calculated in 1), and a more accurate chip position iscalculated (S11 of FIG. 6).

5) Subsequently, as shown in FIG. 4C, the sample power supply 16 stopsthe voltage application, and the alignment exposure of a mask pattern isperformed by a desired acceleration energy based on the chip positionobtained in 4) (S12 of FIG. 6).

An action and effect of the exposure performed as described above willbe described hereinafter.

First, since the global alignment is performed, the frequency of thestage movement 20 can be reduced as shown by arrows of FIG. 8. As aresult, a time required for detecting the mark can be reduced ascompared with the conventional method, and a productivity in theelectron beam exposure can be enhanced.

Secondly, the vernier pattern 202 is exposed based on the positioninformation of the first mark from the wafer layout information file,the positional shift between the vernier pattern 202 and the alignmentpattern 201 is measured, and an alignment error is corrected. Thereby, aprecision in the global alignment can be enhanced.

In the global alignment, all the chips on the wafer are not positionedduring the exposure. Therefore, in the conventional method, after apreliminary wafer is aligned/exposed and the pattern is formed beforethe exposure step, the positional shift of the pattern is inspected, andthe position needs to be corrected during the exposure step.Additionally, the preliminary wafer is a testing substrate subjected toa process flow similar to that of a desired exposure substrate. Suchpreliminary treatment substantially deteriorates an exposure throughput,and also deteriorates the precision of the alignment exposure.

On the other hand, in the first embodiment, after the global alignment,the vernier pattern (second mark) is exposed, and further the alignmenterror from the alignment mark (first mark) can be measured withoutremoving the chip from the apparatus. As a result, the treatment of thepreliminary wafer as a disadvantage of the conventional global alignmentis unnecessary, and the exposure throughput is enhanced. Furthermore,the correction value can be obtained in the apparatus. Therefore, evenwhen the correction value is obtained for each wafer to be exposed, theexposure throughput is not deteriorated, different from the conventionalmethod. As a result, the alignment exposure can be realized with thehigh precision.

Thirdly, the second incident energy in the pattern observation issmaller than the first incident energy during the pattern exposure. As aresult, even when the resist surface is scanned with the beam and thepattern is observed, the latent image (vernier pattern) in the resistexposed with the first incident energy is prevented from beingsuperposed and exposed. Therefore, the latent image can be detected withthe high precision. As a result, it is possible to highly preciselymeasure the positional shift amount between the alignment mark and thevernier pattern.

Particularly, when the second incident energy is set to 3 keV or less,only about 0.3 μm from the surface of the insulator film having athickness of several micrometers on the mark is exposed, and the surfacecan effectively be charged. Moreover, when the second incident energy isset to 1 keV or less, only about 0.05 μm from the resist surface isexposed. This can be regarded as only little exposure, and is moreeffective.

Here, FIG. 9A shows a relation between the second incident energy andcontrast during the pattern observation with respect to the sample shownin FIG. 5A. Here, a contrast C is defined as C=|A−B|/|A+B|. A characterA denotes a signal value from the mark, and B denotes a signal valuefrom portions other than the mark.

As shown in FIG. 9A, when the acceleration voltage is about 3 keV, amaximum contrast is obtained. There are various substrate types.However, with the incident energy substantially of about 3 keV, thevoltage contrast image (FIG. 9B) having a satisfactory contrast isobtained. This is because the resist surface can efficiently be chargedwith this energy as described above.

Fourthly, a bias voltage is applied to the wafer 6 in order to changethe incident energy during the pattern observation and during thepattern exposure. In this case, the electron gun and electron beamoptics for the exposure, and the optics for detecting the positions ofthe latent image and alignment mark can be used in common. As a result,the apparatus configuration can be simplified.

Additionally, in the first embodiment, the energy application from thesample power supply 16 is stopped, and the first incident energy is setto 5 keV when the exposure is performed. However, the energy applicationfrom the sample power supply 16 does not have to be stopped. Theincident energy during the exposure is not limited as long as theelectron is passed through the resist.

Moreover, in the aforementioned embodiment, the stage is moved based onthe position information of the mark 12 (first mark 201) read out fromthe wafer layout information file 118. When a mechanical precisionduring mounting of the wafer 6 onto the stage 7 is insufficient, thesecond mark (vernier pattern) cannot be exposed in the vicinity of themark 12. In this case, the exposure may be performed as follows (see aflowchart of FIG. 10).

1) The exposure control circuit 116 reads the positions of the pluralityof alignment marks (first marks 201) to be detected on the wafer 6 fromthe wafer layout information 118. Subsequently, the exposure controlcircuit 116 issues the command to the stage control circuit 115 andmoves the stage 7. Thereby, the first mark 201 on the wafer 6 ispositioned in the range which can be exposed to the electron beam (S1,S2 of FIG. 10).

2) Subsequently, the exposure control circuit 116 uses the incidentenergy control circuit 119 to change the first incident energy to thesecond incident energy, and scans the region including the first mark201 by the electron beam 14 with the second incident energy. Thesecondary electron generated by the scanning is detected by the detector11. The secondary electron signal detected by the detector 11 isamplified by the detection amplifier 112, and the positional shiftamount calculation circuit 113 calculates the positional shift amount ofthe first mark 201 from the image signal or the waveform signal. Thepositional shift amount is a shift amount between an actual first markposition and a value estimated based on the wafer layout information118. The calculated positional shift amount of the first mark is storedby the exposure control circuit 116 (S5 of FIG. 10).

3) Subsequently, the exposure control circuit 116 exposes the secondmark having the predetermined shape with the first incident energy inthe predetermined position in the vicinity of the first mark. In thiscase, it is meant by the predetermined position in the vicinity of thefirst mark that the position relation between the first and second marksis predetermined and the marks are exposed with the predeterminedrelation. In this case, the exposure control circuit 116 stores thedeflected position of the electron beam 14 and the stage position (S7 ofFIG. 10).

4) Subsequently, the incident energy control circuit 119 is used tochange the first incident energy to the second incident energy, andscans the region including the first and second marks by the electronbeam 14 with the second incident energy. The secondary electrongenerated by the scanning is detected by the detector 11.

The secondary electron signal detected by the detector 11 is amplifiedby the detection amplifier 112, and transmitted as the image signal orthe waveform signal to the positional shift amount calculation circuit113. The positional shift amount calculation circuit 113 calculates thepositional shift amount between the first and second marks from thetransmitted image or waveform signal. The calculated positional shiftamount between the first and second marks is stored by the exposurecontrol circuit 116 (S9 and S10 of FIG. 10).

5) The steps 2 to 4 are performed for the number of all the first marks201 on the wafer 6 to be detected. Similarly as the first embodiment,the correction value is considered, the chip position is calculated, andthe alignment exposure is performed (S14, S15 of FIG. 10).

Even in this method, the effect similar to that of the aforementionedembodiment can be obtained.

Second Embodiment

FIG. 11 is a schematic configuration diagram showing the electron beamexposure apparatus according to a second embodiment of the presentinvention. The control system of the exposure apparatus is similar tothat shown in FIG. 3B of the first embodiment.

In addition to the configuration of the first embodiment, the secondembodiment has the following characteristic configuration. That is, thecharacteristic of the present apparatus lies in that an off-axis opticalmicroscope 15 is disposed. The off-axis optical microscope 15 irradiatesthe mark 12 on the wafer 6 with the laser beam, detects an optical imageby a scattered light or a reflected light, and thereby detects the markposition.

The alignment method in the second embodiment will next be describedwith reference to FIGS. 12A to 12D, and 13. FIGS. 12A to 12D arediagrams showing the movement of the exposure apparatus with thealignment, and FIG. 13 is a flowchart of the alignment method. Theplurality of chips 8 are formed on the wafer 6 to be exposed, and thealignment mark 12 is formed in each chip 8. Here, steps subsequent tothe step of mounting the wafer 6 onto the stage 7 will be described.

1) First, as shown in FIG. 12A, the off-axis optical microscope 15 isused to detect the position of the chip 8. In this case, the detectionof the positions (global alignment) of representative five chips (acentral chip and four peripheral chips) on the wafer 6 is performed. Themark 12 (first mark 201) is moved to right under the microscope 15 andthe position thereof is detected (S1 to S3 of FIG. 13).

2) The positions of all the chips on the wafer 6 are calculated based ona predetermined calculation equation from the chip positions obtainedin 1) (S5 of FIG. 13).

3) Subsequently, as shown in FIG. 12B, the wafer 6 is moved to theposition which can be exposed with the electron beam, andaligned/exposed with the beam based on the chip position calculated in1). In this case, similarly as shown in FIG. 5B, the vernier pattern(second mark) 202 is exposed with the first incident energy beside thealignment mark (first mark) 201 (S6 to S8 of FIG. 13).

The condition of the first incident energy is the same as that of thefirst embodiment, and the subsequent steps are carried out similarly asS6 and the subsequent steps of the first embodiment (FIG. 6).

The action and effect of the exposure performed as described above willbe described hereinafter.

First, since the off-axis optical microscope 15 detects the alignmentmark, the resist on the mark is prevented from being excessivelyexposed.

Secondly, with the global alignment, as shown by the arrows of FIG. 8,the frequency of the stage movement 20 can be reduced. As a result, thetime required for detecting the mark can be reduced as compared with theconventional method. As a result, the productivity in the electron beamexposure can be enhanced.

Thirdly, the vernier pattern 202 is exposed based on the alignmentresult by the optical microscope, the positional shift between thevernier pattern 202 and the alignment pattern 201 is measured, and thealignment error is corrected. Thereby, the positioning precision in theglobal alignment can be enhanced.

As described above, even in the second embodiment, the effect similar tothat of the first embodiment can be obtained.

Third Embodiment

FIG. 14 is a schematic configuration diagram showing the electron beamexposure apparatus according to a third embodiment of the presentinvention. Additionally, the same components as those of FIG. 11 aredenoted with the same reference numerals, and detailed descriptionthereof is omitted. This also applies to subsequent embodiments.

The third embodiment is different from the second embodiment in that thepower supply 16 for applying the voltage to the sample is not disposed,and instead an electron beam scanner 60 for observing the pattern isdisposed. The electron beam scanner 60 for observing the pattern has anelectron gun 61, projection and objective lenses 62 a, 62 b, anddeflector 64, and can scan a desired region on the wafer 6 with anelectron beam having an acceleration energy of 1 keV.

With the apparatus, in the afore-mentioned step 4), the electron beamscanner 60 is used instead of the sample power supply 16, and theperiphery of the vernier pattern is scanned while the energy of theelectron beam incident upon the wafer 6 is decreased to 1 keV. Thereby,the positional shift of each mark can be measured. Therefore, the effectsimilar to that of the first or second embodiment can be obtained.

Additionally, the third embodiment has the apparatus configuration inwhich the sample power supply 16 is not used. However, even when thesample power supply 16 is added to the third embodiment, there is nodisadvantage. For example, the electron beam scanner 60 for observingthe pattern as well as the sample power supply 16 may be used to applythe voltage to the sample. In this case, the acceleration voltage of theelectron beam scanner 60 for observing the pattern may be determined inconsideration of the voltage applied from the sample power supply 16.Even in this case, the effect similar to that of the first embodimentcan be obtained.

Fourth Embodiment

In a fourth embodiment, a method of using a standard mark formed on thestage or a wafer pallet to correct a baseline shift of an alignmentoptics and exposure optics will be described. A charged particle beamexposure apparatus for use in the fourth embodiment has a configurationsimilar to that of the second embodiment.

In the alignment method of the fourth embodiment, first as shown in FIG.15A, the off-axis optical microscope 15 is used to measure the positionof a standard mark 71 formed on a wafer pallet 77. Subsequently, asshown in FIG. 15B, the position of the standard mark 71 on the pallet 77is measured by scanning the electron beam. In this manner, the baselineshift (positional shift) between the alignment optics (off-axismicroscope) and the electron beam optics is measured. Furthermore, thechip position is corrected based on the measured baseline shift, and thepattern exposure and vernier exposure are performed. This respect issimilar to that of the second embodiment.

This method is effective for treating a plurality of wafers. Forexample, when 20 wafers of the same type are treated, the first wafer issubjected to a treatment similar to that of the second embodiment, andonly the baseline shift is calculated with respect to second andsubsequent wafers. When the baseline shift is larger than apredetermined reference value, the treatment described in the first orsecond embodiment may be performed again.

Additionally, in the fourth embodiment, the standard mark 71 is formedon the wafer pallet 77. However, as shown in FIGS. 16A and 16B, astandard mark 72 for correcting the baseline may be disposed on thewafer 6. Even in this case, the effect similar to that of the fourthembodiment can be obtained.

The action and effect of the exposure performed as described above willbe described hereinafter.

First, the baseline shift between the alignment optics (off-axismicroscope) and the electron beam optics can be measured, so that themeasurement precision of the mark position in the alignment optics isenhanced. As a result, the positioning precision in the pattern exposureand vernier exposure is enhanced.

Secondly, a treatment time for treating a plurality of wafers can bereduced. That is, only the first wafer is subjected to the vernierexposure, and only the baseline shift is measured with respect to thesecond and subsequent wafers. In this case, the time for the alignmentcan be reduced, and the productivity in the drawing with the electronbeam can be enhanced.

Fifth Embodiment

In a fifth embodiment, a method of simultaneously performing alignmentand positional shift inspection will be described with reference to FIG.17. The basic configuration of the electron beam exposure apparatus foruse herein is similar to that of the exposure apparatus used in thesecond embodiment. However, as shown in FIG. 17, the fifth embodiment isdifferent from the second embodiment in that two wafer pallets 77 a, 77b for loading the wafer 6 are disposed and an alignment operation andexposure operation are performed at the same time. An exposure method ofthe fifth embodiment will be described hereinafter in detail withreference to FIG. 17.

1) A wafer 6 a is mounted on the pallet 77 a in an alignment chamber.

2) The off-axis optical microscope 15 is used to detect the markposition with respect to the wafer 6 a disposed on the pallet 77 a. Themark positions of eight chips are detected.

3) Subsequently, the pallet 77 a is moved under the electron beamoptics, and the vernier pattern is exposed. Here, the same number ofchips as the chips subjected to the mark position detection, that is,eight chips are subjected to the exposure of the vernier pattern.

4) A wafer 6 b is mounted on the pallet 77 b at the same time as thestep 3).

5) The positional shift inspection of the wafer 6 a disposed on thepallet 77 a, and the mark position detection of the wafer 6 b disposedon the pallet 77 b are carried out at the same time. Here, the number ofthe chips of the wafer 6 b subjected to the mark position detection isthe same as that of chips of the wafer 6 a subjected to the positionalshift detection, and is eight. Therefore, the stage movement frequencyis the same, and each treatment can be performed substantially in thesame time. FIG. 17 shows this state.

6) After the positional shift inspection of the wafer 6 a on the pallet77 a is ended, the chip position is corrected and the alignment exposureis performed similarly as the second embodiment. In this case, the wafer6 b disposed on the pallet 77 b is on standby.

7) After the exposure of the wafer pattern on the pallet 77 a is ended,the wafer 6 b disposed on the pallet 77 b is moved to under the electronbeam optics, and the vernier pattern is exposed. Here, the same numberof chips subjected to the mark position detection, that is, eight chipsare subjected to the exposure of the vernier pattern.

8) The wafer 6 a disposed on the pallet 77 a is retreated simultaneouslywith the step 7), and another wafer 6 is disposed on the pallet 77 a.

9) The positional shift inspection of the wafer 6 a on the pallet 77 a,and the mark position detection of the wafer 6 b on the pallet 77 b arecarried out at the same time. The operation of the steps 6) to 8) isrepeated thereafter.

The characteristic of the fifth embodiment lies in a driving method ofthe stage in the steps 5) and 9). This method will be described withreference to FIGS. 18A to 18C. The alignment optics, electron beamoptics, wafer 6 a disposed on the pallet 77 a, and wafer 6 b disposed onthe pallet 77 b are shown.

FIG. 18A shows a basic arrangement. FIG. 18B shows an example in whichthe pallets 77 a and 77 b are driven in a vertical direction, and FIG.18C shows an example in which the pallet is driven in a horizontaldirection.

For the movement for the alignment and electron beam (vernier) exposure,as shown in the drawings, the pallets 77 a and 77 b are moved in asymmetric direction with respect to a center point P between thealignment optics and the electron beam optics. Even when the stage ismoved at a high speed, a load balance is kept, and it is possible toinhibit the apparatus from vibrating.

As described above, according to the fifth embodiment, the alignment andthe positional shift inspection can be performed at the same time. As aresult, the exposure throughput can be enhanced as compared with thetreatment of the wafers one by one. Moreover, when the loads of twostages are balanced, and the stages are driven, the apparatus can beinhibited from being vibrated by the stage driving. Therefore, the markposition can be detected and the beam can be positioned with the highprecision, and a high-precision alignment can also be realized.

Sixth Embodiment

A sixth embodiment will be described as a modification embodiment of thefifth embodiment with reference to FIG. 19. In the embodiment, twowafers can be loaded on the wafer pallet.

The basic configuration of the electron beam exposure apparatus for usein the sixth embodiment is similar to that of the exposure apparatusused in the second embodiment. However, the sixth embodiment isdifferent from the second embodiment in that a wafer pallet loaded withtwo wafers is disposed and the alignment operation and exposureoperation are carried out at the same time.

The exposure method of the sixth embodiment will be describedhereinafter in detail with reference to FIG. 20. FIG. 20 shows thealignment optics, electron beam optics, wafer pallet 77, positions A andB on the pallet 77, and load/unload positions A and B.

1) The wafer 6 a is loaded in the position A on the pallet 77 in thewafer load/unload position A.

2) The wafer 6 a loaded on the pallet 77 is moved to under the alignmentoptics. In this case, the wafer 6 b is loaded onto the pallet 77.

3) The off-axis optical microscope is used to detect the mark positionwith respect to the wafer 6 a. The mark positions were detected withrespect to eight chips.

4) The wafer 6 a is moved to under the electron beam optics. The vernierpattern is exposed. Here, the same eight chips as the chips subjected tothe mark position detection were subjected to the exposure of thevernier pattern. Furthermore, the positional shift inspection of thewafer 6 a under the electron beam optics, and the mark positiondetection of the wafer 6 b under the alignment optics are performed atthe same time. Here, the number of chips subjected to the mark positiondetection of the wafer 6 b is the same as that of chips subjected to thepositional shift inspection of the wafer 6 a, and is eight. Therefore,the stage movement range becomes the same, and each treatment can beperformed substantially simultaneously. After the positional shiftinspection of the wafer 6 a is ended, the pattern exposure of the waferposition is performed.

5) After the pattern exposure of the wafer 6 a is ended, the wafer 6 ais moved to the load/unload position B, and the wafer 6 a is removed.Simultaneously, the wafer 6 c is loaded in the position A on the pallet77. In this case, the wafer 6 b moves to under the electron beam optics.

6) The pattern of the wafer 6 b is exposed.

7) After the pattern exposure of the wafer 6 b is ended, the wafer 6 bis moved to the load/unload position B, the wafer 6 b is removed, and awafer 6 d is loaded.

Thereafter, the operation of the steps 2) to 7) is repeated.

Additionally, as shown in FIG. 21, two alignment optics may be disposed.In this case, the operation is performed as follows.

1) The wafer 6 a is loaded.

2) The wafer 6 a is aligned.

3) The vernier exposure of the wafer 6 a is performed, the positionalshift inspection of the wafer 6 a is performed simultaneously with thealignment of the wafer 6 b, and subsequently the pattern of the wafer 6a is exposed.

4) The wafer 6 a is removed and the wafer 6 c is loaded.

5) The vernier exposure of the wafer 6 b is performed, the positionalshift inspection of the wafer 6 b and the alignment of the wafer 6 c aresimultaneously performed, and subsequently the pattern exposure of thewafer 6 b is performed.

According to the sixth embodiment, similarly as the fifth embodiment,the alignment can be carried out simultaneously with the positionalshift inspection. As a result, the exposure throughput can be enhancedwith the treatment of the wafers one by one.

Additionally, the present invention is not limited to the respectiveembodiments. The configuration of the exposure apparatus is not limitedto the configuration of FIG. 3A or FIG. 11, and can appropriately bechanged in accordance with specifications. Moreover, the presentinvention is not limited to the electron beam, and can also be appliedto the exposure in which an ion beam is used.

The latent image in the resist described in the embodiments indicatesthat the chemical, electrical, or physical change is generated in theresist by the charged particle beam exposure. Concretely, a change offilm thickness or a change of conductivity is generated by decompositionof a photosensitive material. The present invention can also be appliedeven when the change of the resist (i.e., the latent image) by thecharged particle beam exposure is not remarkably generated. Here, a casein which the latent image by the charging beam is not easily generatedcorresponds to 1) the exposure of the vernier pattern with a smallexposure amount to such an extent that the resist is not exposed, 2) acase in which an Si oxide film, and the like require a large exposureamount, and 3) the use of a resist which does not easily cause a filmthickness change or a conductivity change by the charged particle beamexposure. Even in this case, when the vernier pattern is exposed, and acharged trace is formed on the resist surface, the positional shiftamount between the vernier pattern and the alignment mark can bedetected. FIG. 22 shows the alignment mark image and the voltagecontrast image by a charged trace of the vernier pattern.

Moreover, to measure the alignment error of the vernier pattern andalignment mark in the embodiment, the electron beam may be scanned atrandom in a beam scanning region, or may be scanned in a reciprocatingdirection. In this manner, a distortion of the signal waveform dependingon the beam scanning direction can be reduced.

As described above in detail, according to the present invention, whenthe alignment mark is detected with the optical microscope, the resiston the mark is not excessively exposed. Moreover, the vernier pattern isexposed based on the position information of the alignment mark, thepositional shift between the vernier pattern and the alignment patternis measured, and the alignment error is corrected, so that the alignmentexposure can be realized with the high precision.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

What is claimed is:
 1. A charged particle beam exposure apparatus,comprising: a beam gun which emits a charged particle beam; a projectionoptics which shapes said charged particle beam and projects a desiredpattern; an incident energy control circuit which controls an incidentenergy of said projection optics; a sample stage loaded with a sample inwhich an image projected from said projection optics is to be formed, aplurality of first marks are formed beforehand, and a plurality ofsecond marks are exposed to said charged particle beam with a firstincident energy by said projection optics in the vicinity of saidplurality of first marks; a detector to detect an electron signalgenerated from a region including said plurality of first marks and saidplurality of second marks, when said region is scanned with a secondincident energy different from said first incident energy; a calculationcircuit which calculates a positional shift amount between saidplurality of first marks and said plurality of second marks from saiddetected electron signal; a correction circuit which corrects positionsof said plurality of first marks on said sample based on said calculatedpositional shift amount; and an exposure control circuit which alignssaid desired pattern based on corrected positions of said plurality offirst marks.
 2. The charged particle beam exposure apparatus accordingto claim 1, further comprising an optical microscope which measures saidpositions of said plurality of first marks.
 3. The charged particle beamexposure apparatus according to claim 2, wherein said optical microscopeto measure said positions of said plurality of first marks measures someof the positions of said plurality of first marks, and calculates theother positions of said plurality of first marks based on measurementresults of said some positions.
 4. The charged particle beam exposureapparatus according to claim 1, wherein said second incident energy issmaller than said first incident energy.
 5. The charged particle beamexposure apparatus according to claim 4, wherein said second incidentenergy is 3 keV or less.
 6. The charged particle beam exposure apparatusaccording to claim 1, further comprising a power supply which applies avoltage to said sample in order to allow said first incident energy andsaid second incident energy to differ from each other.
 7. The chargedparticle beam exposure apparatus according to claim 1, furthercomprising a charged particle beam optics to which said second incidentenergy is inputted separately from said projection optics in order toallow said first incident energy and said second incident energy todiffer from each other.
 8. The charged particle beam exposure apparatusaccording to claim 1, wherein said first mark is formed on the surfaceof said sample, and said second mark is a latent image formed on aresist layer disposed on said sample.
 9. The charged particle beamexposure apparatus according to claim 1, wherein an acceleration voltageof said beam gun is in a range of 1 keV to 8 keV.
 10. The chargedparticle beam exposure apparatus according to claim 1, furthercomprising a reference mark for correcting a baseline shift on saidsample stage.